According to https://d2.lc/IAS/ it seems completely unnecessary to have anything more than 30 IAS on a Grief PB for a Paladin. Attacks per second are the same regardless of 30 or 40 IAS. Why is everybody paying premium for high IAS Griefs?

this is quite exaggerated
e.g. no fana zeal hits max bp at 72 which needs loh + highlord + 32 ias pb

Also, other characters use grief PB, not just Paladin.

Grief PB 30 or 40 IAS
LoH+Highlord = 40 extra IAS
Fana Lvl 27
Zeal Lvl 27

put it in the calc https://d2.lc/IAS/

no change in attacks/s regardless of 30 or 40?!

as was stated above, Paladin's are not the only characters to use Grief Phase Blades.

But for a Paladin as an example, lv 27 Fanaticism with 30 IAS Grief for zeal you need 9% more IAS for max break point. a 39/40 ias PB will give you the max break point. You no longer need to use Hilords or LoH to get to the max breakpoint, which lets you use a different amulet and gloves than can give you more benefit to your zealer than using those two items.

plus, an expensive Grief also has its value determined on the +damage roll too, not jus the the +ias%

Where can I learn more about IAS breakpoints? Is the IAS calculator at https://d2.lc/IAS/ wrong, because it tells me that there is no difference between a 30 and 40 IAS Grief PB.

Aparently 2grief best barb wepons
Also some weird druids

Using the same calculator. You had Hilords and LOH added into your calculations. This is with no other IAS beyond Fanaticism 27 and 30% From Grief.

Ahh, weird. If you select "Show IAS Table" it shows something different than on the bottom of the form #wtf